1. Field of the Invention
This invention relates to a refrigerating cycle system suitable for an automotive air conditioner, which includes a hot-gas bypass for introducing gaseous refrigerant (hot gas), discharged from a compressor, directly into an evaporator while bypassing a condenser at a heating state so that the gaseous refrigerant radiates heat in the evaporator.
2. Description of the Related Art
In a conventional automotive air conditioner, hot water (engine cooling water) is circulated in a heat exchanger for heating at a winter season heating state, and air is heated by exchanging heat with the hot water in the heat exchanger. In this sytem, there is a case where hot water does not have a temperature sufficient for raising the temperature of air, which is to be blown into a compartment, up to a desired level. This results in insufficient heating capacity.
To solve this problem, JP-A-5-223357 proposes a refrigerating cycle system using a hot-gas bypass so as to enhance the heating capacity. Specifically, a hot-gas bypass passage is provided so that gaseous refrigerant (hot gas) that is discharged from a compresser pypasses a condenser and directly communicates with an evaporator, and a decompressing part is provided in the hot-gas bypass passage. Accordingly, even when a hot water temperature is lower than a specific temperature as in an engine starting state, gaseous refrigerant can be directly introduced into the evaporator after being decompressed by the decompressing part in the hot-gas bypass passage so that heat is radiated from gaseous refrigerant toward air in the evaporator.
In the system described above, an amount of work of compression in the compressor is ideally transformed into a radiation amount (heating capacity) in the evaporator. Therefore, a heat loss amount (radiation amount) radiated toward an outside through a pipe that defines therein the hot-gas bypass passage directly lessens the heating capacity. Especially, in a winter season, there arises a large difference between a temperature of gaseous refrigerant immediately after discharged from the compressor, which can, for instance, be 70.degree. C. at a discharge pressure of 20 kgf/cm.sup.2, and an outside air temperature, which can, for instance, be -20.degree. C. Therefore, the longer the pipe length of the hot-gas bypass passage in which refrigerant flows before decompression becomes, the more the heat loss amount of gaseous refrigerant in the hot-gas bypass passage is increased.
In addition, when refrigerant has a temperature of 70.degree. C. and a pressure of 20 kgf/cm.sup.2 immediately after discharged from the compressor, under a condition with an outside air temperature of -20.degree. C., the refrigerant can have the temperature of 40.degree. C. and a pressure of 2 kgf/cm.sup.2 after decompressed by the decompressing part in the hot-gas bypass passage and have a temperature of -10.degree. C. and a pressure of 1 kgf/cm.sup.2 at the outlet side of the evaporator.
To the contrary, because the condenser is exposed to an ambient atmosphere with a temperature of -20.degree. C., a temperature of refrigerant is cooled down to -20.degree. C. to be equal to the ambient temperature, within the condenser, and accordingly refrigerant is transformed into a liquid state with a saturation pressure (0.5 kgf/cm.sup.2 G) that corresponds to the temperature. Therefore, refrigerant immediately after decompressed by the decompressing part in the hot-gas bypass passage has a high temperature and a high pressure as compared to those of refrigerant within the condenser. Consequently, refrigerant tends to flow from the hot-gas bypass passage into the condenser.
To solve this problem, in the above-described system, a check valve is disposed on an outlet side of a receiver that is disposed on the outlet side of the condenser. However, in an automotive air conditioner, the condenser and the receiver are usually installed in an engine room fore most portion (ahead of a radiator). Therefore, when the check valve is provided adjacently to the receiver, it is necessary to provide a relatively long pipe for connecting a confluence point between the evaporator and the hot-gas bypass passage outlet portion and the check valve. As a result, liquid refrigerant gathers within the pipe between the confluence point and the check valve. This causes shortage of a refrigerant amount circulating when the hot-gas bypass passage is opened, resulting in deterioration of the heating capacity and an abnormal increase in temperature of gaseous refrigerant discharged from the compressor. In addition, the check valve along the refrigerant pipe requires an exclusive joint, resulting in increased cost.